Will this reading be on the test?

My friend and colleague Brad Wright has included several plugs for this blog on his own blog.  Brad is interested in religion, so here's a finding for him, from a 1965 Gallup Poll.  The survey asked people whether they'd done various things--there was no particular logic to the list, which included flying in a plane, eating caviar, and betting money at a race track (more common than I would have guessed).  One of the items was "read the Bible through--every word."  20% of the respondents said they had.  The straightforward interpretation is that 20% of Americans had read the Bible all the way through, but I find that hard to believe.  The Bible is a long book, and as a college professor I have a good sense of the chance that people will read long books all the way through.

Another possibility is "social desirability bias"--people are giving the answer that they think they "ought" to give, rather than telling the truth.  If the question involved general frequency of reading the Bible or attending religious services, social desirability might be an important factor.  But I don't think many people imagine that the world will think worse of them if they skipped a few of the minor prophets.  Also, the way that the question was asked cut down on the risk--it gave them a list and asked them to read off the letters designating the things they had done.  So you didn't have to explicitly say "no"--you just had to leave the letter "p" off of your list. 

A third  possibility, which I find the most plausible, is that most of these people thought they had read the Bible all the way through, even though they probably hadn't actually done so.  How would this be possible?  My guess is that many people who attended church frequently, or had done so at some point in their lives, figured that given the Bible reading involved they must have covered it all over the course of time, even if not in consecutive order. 

Another question in the list asked if you'd read a book all the way through since leaving school.  Of the people who said they hadn't, 12% said they'd read every word of the Bible.  People who'd gone to college were most likely to say that they'd read the entire Bible (26%), but people who'd just reached grades 8-11 were almost as likely (22%).  Among high school graduates who hadn't attended college, it was only 15%.